Devices of the present type are used for a polyaxial, rigid screw connection, particularly in the region of the spinal column, for example for pedicle screws or pedicle hooks. However, they can also be used generally for plate osteosynthesis. In addition, uses for external fixators as well as for intervertebral implants are also possible.
Such a device is already known from U.S. Pat. No. 6,235,003, in which a pivotable, ring-shaped insert is present between the screw head and the bore of the bone plate, which insert can be compressed and expanded by means of a slit, in order to thereby achieve improved fixation between screw and plate. The disadvantages of this known device are multiple. The axially rigid insert, configured to be circular, can turn with the screw as it is turned, and thereby prevents locking. Moreover, the insert can also twist completely within the plate bore, so that it then comes to rest with the wrong side up (inner cone narrows in the wrong direction).
The above discussion of the state of the art takes place merely to explain the surrounding field of the invention, and does not mean that the cited prior art was actually published or publicly known at the time of this application or its priority.